The present invention relates to an oil and gas industry, and more particularly to a drilling jack-up platform that can be used to develop sub-salt gas wells through existing shallow wells or to drill entirely new wells.
In the past, a large number of fixed platforms have been used in the oil and gas industry for exploration and production of natural resources. The wells were drilled and pipelines laid for connection to the wells to extract the valuable hydrocarbon fuel from offshore locations, often at a considerable cost to the developer. Some of these platforms and pipelines are quite old; they were designed for small platform rigs that can support drilling operations at 8,000-20,000 feet. However, these old platforms cannot simultaneously support exploration and production from the high-pressure deep formations of the sub-salt environment.
In order to continue drilling and production using the existing wells, additional process equipment is required for pre-treating of the produced fluids while utilizing the existing process train. If such equipment is to be installed on the old platforms, it will utilize any remaining topsides capacity of these platforms.
The present invention was conceived to assist the platform owners to continue exploration and production from the existing fixed platforms, while providing support for the necessary drilling equipment and consumables independently of the fixed platform. The present invention utilizes a jack-up design with a cantilever drill floor that extends over the fixed platform with existing wells to support deeper drilling and stimulate production from the old wells.
The use of cantilevers on drill platforms is not entirely new. One of the known jack-up platforms utilizing cantilever is disclosed in U.S. Pat. No. 6,171,027 issued on Jan. 9, 2001 for xe2x80x9cCantilevered Jack-Up Platform.xe2x80x9d According to this patent, one cantilever is provided on a jack-up platform. The cantilever moves in a longitudinal direction, towards and away from the platform, as well as in a transverse direction. A drilling platform, from which the drilling operations are performed, along with the derrick, and other drilling equipment, is fixedly positioned on the cantilever. It moves along with the cantilever longitudinally and transversely. The cantilever is supported by supporting members which slide by means of cylinders over rails that are provided on the jack-up platform.
While this design is an improvement over old cantilever designs, there is still a limit to the number of wells that can be drilled with the use of the drilling equipment positioned on the platform according to the ""027 patent. However, by using only one cantilever assembly and one drilling floor, the design of the ""027 patent does not permit conducting very efficient drilling operations.
The present invention contemplates elimination of drawbacks associated with the prior art and provision of a self-elevating drilling jack-up platform that can be positioned adjacent to existing platforms, as well as in undeveloped locations to support drilling and recompletion operations down to 25,000-35,000 feet from dual cantilever drilling assemblies. Primary among the improvements over the prior art is the fact that two drilling cantilevers are provided on the jack-up unit, allowing for much faster well development. Further, one of the advances that makes having two cantilevers viable is the use of a truss structure for the cantilever. This has led to weight savings that have kept the reaction forces imparted by the cantilever onto the jack-up manageable by a typically sized jack-up hull. Also, the cantilevers are infinitely adjustable within their extreme limits of motion in the horizontal plane. Also, the slim geometry of each cantilever will allow it to work over platforms in deeper water than a unit of similar leg length having a broader cantilever. This is because the slim cantilever can fit between the process equipment module and quarter""s module of a fixed platform and be just above a well bay. A broader cantilever could be forced to reach from high above the well bay.
It is, therefore, an object of the present invention to provide a self-elevating drilling unit that can be used for completing wells in deep salt areas.
It is another object of the present invention to provide a jack-up platform that uses twin cantilevers extendable from the aft of the platform, while being held down on the platform by a stationary hold down beam.
It is a further object of the present invention to provide a jack-up drilling platform wherein twin cantilever structures move independently relative to the platform in a longitudinal direction, extending outwardly from the platform, and in a transverse direction, perpendicular to the first direction.
These and other objects of the present invention are achieved through a provision of a jack-up platform that is positionable adjacent an existing stationary platform at an offshore location. A pair of cantilever assemblies are mounted on the jack-up platform and are secured at one of their ends to the jack-up platform by a hold down beam that extends over and across the cantilever assemblies. Each cantilever assembly supports drilling and production operations, as necessary, while capable of performing simultaneous drilling operations on an 8 feetxc3x978 feet well spacing, if necessary.
The cantilever assemblies slide on lower longitudinal and transverse roller assemblies that are positioned on a deck of the jack-up platform. Upper longitudinal and transverse roller assemblies are mounted between the upper surfaces of the cantilevers beams and the hold down beam. The upper roller assemblies allow the cantilever beams to slide in relation to the hold down beam, while being retained in a secure relation to the jack-up platform.
A movable strut engages the deck of the jack-up hull and the hold down beam and slides on rollers in relation to the hold down beam. A lower end of the strut is guided by a bracket mounted on a deck of the jack-up platform. The strut engages the hold down beam and deck when the cantilever assemblies are extended to decrease the deflection of the hold down beam.